In response to recent progress in information processing apparatus development and in internationalization, there are an increasing number of chances to view and listen to content in a second language and to make a call in the second language through a telephone call application installed in a personal computer. In these situations, methods are disclosed by which voice signals in a second language, which are an example of input signals, are controlled so that the voice signals are made easy to listen. In, for example, Japanese Laid-open Patent Publication No. 10-133678, a technology is disclosed that makes an input voice easy to understand by extracting a sound period from a voice signal and adding a silent period to the back end of the sound period. It is known that the user usually performs repetitive endophasia in which the user reads back a word that the user has heard in a hard-to-understand second language through an internal speech with no audible vocalization (see Sinozuka Katsumasa, “Listening Power in Second language and Working Memory” transactions No. 40, 2008 at Department of English literature, Graduate School of Literature, Seijo University, for example). Thus, to understand a second language, it is important to ensure silent periods used in repetitive endophasia.